1. Field of the Invention
The invention is directed to purified and isolated novel SIGIRR polypeptides and fragments thereof, the nucleic acids encoding such polypeptides, processes for production of recombinant forms of such polypeptides, antibodies generated against these polypeptides, fragmented peptides derived from these polypeptides, and uses thereof.
2. Description of Related Art
1. IL-1 and IL-1R
Interleukin-1 (IL-1) is a member of a large group of cytokines whose primary function is to mediate immune and inflammatory responses. There are seven known members of the IL-1 ligand family which include IL-1 alpha (IL-1α), IL-1 beta (IL-1β), IL-1 receptor antagonist (IL-1ra), IL-1 delta (IL-1δ), and IL-18 (previously known as IGIF and sometimes IL-1 gamma), IL-1 epsilon (IL-1ε), and IL-1 zeta (IL-1ζ). IL-1 that is secreted by macrophages is actually a mixture of mostly IL-1β and some IL-1α (Abbas et al., 1994). IL-1α and IL-1β, which are first produced as 33 kD precursors that lack a signal sequence, are further processed by proteolytic cleavage to produce secreted active forms, each about 17 kD. Additionally, the 33 kD precursor of IL-1α is also active. Both forms of IL-1 are the products of two different genes located on chromosome 2. Although the two forms are less than 30 percent homologous to each other, they both bind to the same receptors and have similar activities.
IL-1ra, a biologically inactive form of IL-1, is structurally homologous to IL-1 and binds to the same receptors. Additionally, IL-1ra is produced with a signal sequence which allows for efficient secretion into the extracellular region where it competitively competes with IL-1 (Abbas et al., 1994).
The IL-1 type I receptor mediates the biological effects of IL-1. Activities attributed to IL-1α and IL-1β include induction of inflammatory cytokines and other inflammatory responses including prostaglandins, nitric oxide, metalloproteinases, adhesion molecules, acute phase proteins, hematopoiesis, fever, bone resorption, and Th2 cell growth and differentiation.
IL-1 has been implicated in chronic inflammatory diseases, such as rheumatoid arthritis and inflammatory bowel disease. There is increasing evidence that IL-1 plays a role in osteoporosis. All of these activities are initiated by the signaling function of the cytoplasmic portion of the type I IL-1R.
IL-18 is a homolog of IL-1α and IL-1β, and may mediate its activities via a receptor homologous to the IL-1R. IL-18 acts as a stimulator of Th1 cell growth and differentiation, and is a potent inducer of γ-interferon production from Th1 cells. It enhances NK cell killing activity. It has been implicated in septic shock, liver destruction, inflammatory bowel disease, and diabetes.
The IL-1 ligands bind to two IL-1 receptors, which are members of the Ig superfamily. IL-1 receptors include the 80 kDa type I receptor (IL-1RI), and a 68 kDa type II receptor (IL-1RII). IL-1 ligands can also bind to a soluble proteolytic fragment of IL-1RII (sIL-1RII) (Colotta et al., 1993).
IL-1 receptors are members of the large Ig superfamily of cytokine receptors, many of which mediate the response of immune system cells, in particular lymphocytes. In recent years, members of the ligands that bind to these receptors have been discovered at an accelerated pace. The increase in the number of known IL-1 ligands has been largely due to the advent of gene cloning and sequencing techniques. Amino acid sequences deduced from nucleotide sequences are considered to represent IL-1 ligands if they share homology with other known IL-1 ligands.
The major source of IL-1 is the activated macrophage or mononuclear phagocyte. Other cells that produce IL-1 include epithelial and endothelial cells (Abbas et al., 1994). IL-1 secretion from macrophages occurs after the macrophage encounters and ingests gram-negative bacteria. Such bacteria contain lipopolysaccharide (LPS) molecules, also known as endotoxin, in the bacterial cell wall. LPS molecules are the active components that stimulate macrophages to produce tumor necrosis factor (TNF) and IL-1. In this case, IL-1 is produced in response to LPS and TNF production. At low concentrations, LPS stimulates macrophages and activates B-cells and other host responses needed to eliminate the bacterial infection; however, at high concentrations, LPS can cause severe tissue damage, shock, and even death.
The biological functions of IL-1 include activating vascular endothelial cells and lymphocytes, local tissue destruction, and fever (Janeway et al., 1996). At low levels, IL-1 stimulates macrophages and vascular endothelial cells to produce IL-6, upregulates molecules on the surface of vascular endothelial cells to increase leukocyte adhesion, and indirectly activates inflammatory leukocytes by stimulating mononuclear phagocytes and other cells to produce certain chemokines that activate inflammatory leukocytes. Additionally, IL-1 is involved in other inflammatory responses such as induction of prostaglandins, nitric oxide synthetase, and metalloproteinases. These IL-1 functions are crucial during low level microbial infections. However, if the microbial infection escalates, IL-1 acts systemically by inducing fever, stimulating mononuclear phagocytes to produce IL-1 and IL-6, increasing the production of serum proteins from hepatocytes, and activating the coagulation system. Additionally, IL-1 does not cause hemorrhagic necrosis of tumors, suppress bone marrow stem cell division, and IL-1 is lethal to humans at high concentrations.
IL-1 mediated cellular signaling often involves a molecular activation cascade, during which a receptor propagates a ligand-receptor mediated signal by specifically activating intracellular kinases which phosphorylate target substrates. IL-1 mediated cellular signaling may result in the activation of the transcription factors NFkB and AP1 (Stylianou et al., Int. J. Biochem. Cell Biol. 30: 1075-1079, 1998), the protein kinases Jun N-terminal kinase and p38 map kinase (O'Neill et al., J. Leukoc. Biol. 63:650-657, 1998), the enzymes COX-2 leading to prostaglandin production (Crofford, J. Rheumatol. 24 Suppl. 49:15-19, 1997) and iNOS leading to nitric oxide production (Alexander, Nutrition 14: 376-90, 1998), and inflammation in general.
Given the important function of IL-1 and IL-1R, there is a need in the art for additional cytokine receptors similar to the IL-1R family. Despite the growing body of knowledge, there is still a need in the art for the identity and function of proteins involved in cellular and immune responses.
2. Protein Identification
In another aspect, the identification of the primary structure, or sequence, of an unknown protein is the culmination of an arduous process of experimentation. In order to identify an unknown protein, the investigator can rely upon a comparison of the unknown protein to known peptides using a variety of techniques known to those skilled in the art. For instance, proteins are routinely analyzed using techniques such as electrophoresis, sedimentation, chromatography, sequencing and mass spectrometry.
In particular, comparison of an unknown protein to polypeptides of known molecular weight allows a determination of the apparent molecular weight of the unknown protein (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6d ed. 1991)). Protein molecular weight standards are commercially available to assist in the estimation of molecular weights of unknown protein (New England Biolabs Inc. Catalog: 130-131, 1995; J. L. Hartley, U.S. Pat. No. 5,449,758). However, the molecular weight standards may not correspond closely enough in size to the unknown protein to allow an accurate estimation of apparent molecular weight. The difficulty in estimation of molecular weight is compounded in the case of proteins that are subjected to fragmentation by chemical or enzymatic means, modified by post-translational modification or processing, and/or associated with other proteins in non-covalent complexes.
In addition, the unique nature of the composition of a protein with regard to its specific amino acid constituents results in unique positioning of cleavage sites within the protein. Specific fragmentation of a protein by chemical or enzymatic cleavage results in a unique “peptide fingerprint” (D. W. Cleveland et al., J. Biol. Chem. 252:1102-1106, 1977; M. Brown et al., J. Gen. Virol. 50:309-316, 1980). Consequently, cleavage at specific sites results in reproducible fragmentation of a given protein into peptides of precise molecular weights. Furthermore, these peptides possess unique charge characteristics that determine the isoelectric pH of the peptide. These unique characteristics can be exploited using a variety of electrophoretic and other techniques (T. D. Brock and M. T. Madigan, Biology of Microorganisms 76-77 (Prentice Hall, 6d ed. 1991)).
Fragmentation of proteins is further employed for amino acid composition analysis and protein sequencing (P. Matsudiara, J. Biol. Chem. 262:10035-10038, 1987; C. Eckerskorn et al., Electrophoresis 1988, 9:830-838, 1988), particularly the production of fragments from proteins with a “blocked” N-terminus. In addition, fragmented proteins can be used for immunization, for affinity selection (R. A. Brown, U.S. Pat. No. 5,151,412), for determination of modification sites (e.g. phosphorylation), for generation of active biological compounds (T. D. Brock and M. T. Madigan, Biology of Microorganisms 300-301 (Prentice Hall, 6d ed. 1991)), and for differentiation of homologous proteins (M. Brown et al., J. Gen. Virol. 50:309-316, 1980).
In addition, when a peptide fingerprint of an unknown protein is obtained, it can be compared to a database of known proteins to assist in the identification of the unknown protein using mass spectrometry (W. J. Henzel et al., Proc. Natl. Acad. Sci. USA 90:5011-5015, 1993; D. Fenyo et al., Electrophoresis 19:998-1005, 1998). A variety of computer software programs to facilitate these comparisons are accessible via the Internet, such as Protein Prospector (Internet site: prospector.uscf.edu), Multildent (Internet site: www.expasy.ch/sprot/multiident.html), PeptideSearch (Internet site: www.mann.embl-heiedelberg.de . . . deSearch/FR_PeptideSearch Form.html), and ProFound (Internet site: www.chait-sgi.rockefeller.edu/cgi-bin/prot-id-frag.html). These programs allow the user to specify the cleavage agent and the molecular weights of the fragmented peptides within a designated tolerance. The programs compare these molecular weights to protein molecular weight information stored in databases to assist in determining the identity of the unknown protein. Accurate information concerning the number of fragmented peptides and the precise molecular weight of those peptides is required for accurate identification. Therefore, increasing the accuracy in determining the number of fragmented peptides and their molecular weight should result in enhanced likelihood of success in the identification of unknown proteins.
In addition, peptide digests of unknown proteins can be sequenced using tandem mass spectrometry (MS/MS) and the resulting sequence searched against databases (J. K. Eng, et al., J. Am. Soc. Mass Spec. 5:976-989 (1994); M. Mann and M. Wilm, Anal. Chem. 66:4390-4399 (1994); J. A. Taylor and R. S. Johnson, Rapid Comm. Mass Spec. 11:1067-1075 (1997)). Searching programs that can be used in this process exist on the Internet, such as Lutefisk 97 (Internet site: www.lsbc.com:70/Lutefisk97.html), and the Protein Prospector, Peptide Search and ProFound programs described above. Therefore, adding the sequence of a gene and its predicted protein sequence and peptide fragments to a sequence database can aid in the identification of unknown proteins using tandem mass spectrometry.
Thus, there exists a need in the art for polypeptides suitable for use in peptide fragmentation studies, for use in molecular weight measurements, and for use in protein sequencing using tandem mass spectrometry.